Allows settings to be overwritten on a per-project base

If you create a “settings” area on your Project.sublime-project file and 
you override settings of the original RubyTest.sublime-settings file, it
reads that instead.
Added optional 'terminal_encoding' config parameter

Fixes [Decode error - output not utf-8] error for Windows users with
national character sets. Updated README file to reflect the change.
'utf-8' encoding set as default.
Sublime 3 support (backward-compatible with Sublime 2)
Merge pull request #239 from fcoury/override_settings

Allows settings to be overwritten on a per-project base
Merge pull request #241 from EugZol/master

Added optional 'terminal_encoding' config parameter. Fixes #211
Merge pull request #242 from EugZol/sublime-3

Sublime 3 support (backward-compatible with Sublime 2)
Merge remote-tracking branch 'upstream/master'